Render on GPU from command line on Ubuntu server
Whether to or to not use the GPU is a setting saved in the .blend file that you render. Under the "Render" tab in the "Properties" Panel, you can set which compute device the file will render with (CPU or GPU). Note: if you aren't editing on a computer with a valid GPU, then that setting will not appear as an option. If you save the .blend file with that setting, then the command line will render with whatever compute device you specified. (blender -b file.blend [[-args]]) Unfortunately, this cannot be set directly through the command line.

Blender Command Line Arguments List.